The present invention relates generally to the bulk packaging of integrated circuits. More particularly, the invention relates to processes that facilitate panel testing of leadless IC packages that use a conductive substrate.
A leadless leadframe package (LLP) is a relatively new integrated circuit package design that contemplates the use of a metal (typically copper) leadframe type substrate structure in the formation of a chip scale package (CSP). As illustrated in FIG. 1, in typical leadless leadframe packages, a copper leadframe strip or panel 101 is patterned (typically by stamping or etching) to define a plurality of arrays 103 of chip substrate features 105. Each chip substrate feature 105 includes a die attach pad 107 and a plurality of contacts 109 disposed about their associated die attach pad 107. Very fine tie bars 111 are used to support the die attach pads 107 and contacts 109.
During assembly, dice are attached to the respective die attach pads and conventional wire bonding is used to electrically couple bond pads on each die to their associated contacts 109 on the leadframe strip 101. After the wire bonding, a plastic cap is molded over the top surface of the each array 103 of wire bonded dice. The dice are then singulated and tested using conventional sawing and testing techniques. The dice cannot be tested prior to singulation since the tie bars remain in place and therefor electrically connect the contacts 109 until the devices are separated.
FIG. 2 illustrates a typical resulting leadless leadframe package. The die attach pad 107 supports a die 120 which is electrically connected to its associated contacts 109 by bonding wires 122. A plastic cap 125 encapsulates the die 120 and bonding wires 122 and fills the gaps between the die attach pad 107 and the contacts 109 thereby serving to hold the contacts in place. It should be appreciated that during singulation, the tie bars 111 are cut and therefore the only materials holding the contacts 109 in place is the molding material. The resulting packaged chip can then be surface mounted on a printed circuit board or other substrate using conventional techniques.
Although leadless leadframe packaging has proven to be a cost effective packaging arrangement, there are continuing efforts to further reduce the costs associated with packaging. One persistent issue in packaging generally is the need and desire to test the packaged devices. In high density packaging applications such as some of the state of the art leadless packaging, it would be advantageous to be able to test the devices in panel form rather than individually after singulation.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, a variety of techniques for electrically debussing conductive substrate panels used in the formation of a matrix of leadless integrated circuit packages are described. Generally, a matrix of leadless packages are fabricated in panel form on a conductive substrate panel. The substrate panel has one or more arrays of device areas thereon. Each device area includes a plurality of contacts formed from the substrate panel and which are electrically connected to an associated die (which is optionally supported by a die attach pad formed from the same substrate panel). The conductive substrate panel also defines a plurality of tie bars that support the contacts during fabrication. After the dice have been mounted and electrically connected to their associated contacts, at least one cap is molded over the substrate panel. Each cap is arranged to encapsulate an array of the devices. With this arrangement, the molding material serves to hold the contacts and dice in place relative to one another. After the molding operation, portions of the tie bars are removed to electrically isolate the contacts from one another while leaving sufficient portions of the molded substrate structure in tact to facilitate handling the structure in panel form.
With the described arrangement, the packaged devices may be tested in panel form. After testing and any other desired panel based operations, the packaged devices may be separated using conventional techniques. The removal of the tie bars can be accomplished by any suitable technique including, for example, sawing or etching.